{"gene":"FDX2","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2010,"finding":"FDX2 (Fdx2), but not FDX1 (Fdx1/adrenodoxin), is essential for heme A and Fe/S protein biosynthesis in human mitochondria. FDX2 deficiency impairs Fe/S protein biogenesis, leading to increased cellular iron uptake and iron accumulation in mitochondria. Conversely, FDX2 is unable to efficiently reduce mitochondrial cytochromes P450 or convert steroids, functions specific to FDX1.","method":"RNAi-mediated depletion of FDX1 or FDX2 in human cells, with biochemical readouts for heme A, Fe/S cluster assembly, steroid conversion, and iron homeostasis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockdown with multiple orthogonal biochemical readouts, independently establishing substrate specificity of FDX2 vs FDX1","pmids":["20547883"],"is_preprint":false},{"year":2017,"finding":"Both FDX1 and FDX2 bind the cysteine desulfurase complex (NFS1/ISD11/Acp) via residues near their Fe-S clusters, but FDX2 binds the complex more tightly than FDX1 (by isothermal titration calorimetry). In vitro, reduced FDX2 supports Fe-S cluster assembly on ISCU at a faster rate than FDX1. FDX2 donates electrons to the cysteine desulfurase complex, resulting in conversion of L-cysteine to L-alanine and sulfide generation.","method":"NMR spectroscopy (protein-protein interaction mapping), isothermal titration calorimetry, in vitro Fe-S cluster assembly assay on ISCU","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal in vitro methods (NMR, ITC, reconstitution assay) in a single study","pmids":["28001042"],"is_preprint":false},{"year":2020,"finding":"FDX2, together with its reductase FDXR (NADPH-coupled), provides electrons required for reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 in an IBA57-dependent manner, enabling maturation of mitochondrial [4Fe-4S] proteins. This electron transfer step is distinct from FDX2's earlier role in [2Fe-2S] cluster synthesis on ISCU2. FDX1 and other cellular reducing systems cannot substitute for FDX2 in this step.","method":"In vitro reconstitution of [4Fe-4S] aconitase maturation without artificial reductants, using purified components; Mössbauer spectroscopy; biochemical complementation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with defined components, multiple spectroscopic validations, specificity confirmed by negative controls (FDX1, other reductants)","pmids":["32817474"],"is_preprint":false},{"year":2022,"finding":"FDX2, but not FDX1, is required for Fe-S protein maturation; FDX1 is specific for steroidogenesis, heme a biosynthesis, and lipoyl cofactor biosynthesis (providing electrons to lipoyl synthase). The distinct substrate specificity of each ferredoxin is determined by small conserved sequence motifs; swapping these motifs exchanges their target specificities.","method":"RNAi depletion in human cells, in vitro biochemical assays, domain-swap mutagenesis, functional assays for steroidogenesis/lipoylation/Fe-S assembly","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including mutagenesis, in vitro assays, and cell-based depletion; replicates and extends earlier PNAS 2010 findings","pmids":["36280795"],"is_preprint":false},{"year":2013,"finding":"A homozygous loss-of-function mutation in FDX1L (FDX2; c.1A>T disrupting the ATG initiation codon) causes severe reduction of Fdx2 protein in patient muscle and fibroblast mitochondria, resulting in severely impaired activities of Fe-S-dependent respiratory chain complexes I, II, III and mitochondrial aconitase, establishing FDX2 as the second component of the Fe-S cluster biogenesis machinery in human muscle.","method":"Exome sequencing + homozygosity mapping; enzyme activity assays in patient skeletal muscle; western blot of patient mitochondria","journal":"European journal of human genetics : EJHG","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function patient mutation with specific biochemical phenotype (enzyme activities) and protein quantification; single lab, no in vitro reconstitution","pmids":["24281368"],"is_preprint":false},{"year":2018,"finding":"A homozygous missense mutation in FDX2 (c.431C>T, p.P144L) causes severely reduced FDX2 protein expression (normal mRNA, reduced protein by western blot) in patient muscle, with an unusual pattern of succinate dehydrogenase and cytochrome c oxidase deficiency and iron accumulation on muscle biopsy, confirming FDX2's essential role in Fe-S cluster biogenesis in vivo.","method":"Genetic mapping + whole exome sequencing; RT-PCR; western blot of patient muscle; muscle biopsy with histochemical and iron staining","journal":"Brain : a journal of neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient loss-of-function with protein quantification and specific biochemical readouts, single lab","pmids":["30010796"],"is_preprint":false},{"year":2024,"finding":"The pathogenic P144L mutation of FDX2 negatively affects the FDXR-dependent electron transfer pathway from NADPH to FDX2 by altering the protein-protein recognition between FDX2 and its physiological electron donor FDXR, thereby reducing FDX2's capacity to assemble both [2Fe-2S] and [4Fe-4S] clusters. The C-terminal tail of FDX2 plays a functional role in electron transfer between FDX2 and FDXR.","method":"Structural characterization (NMR, EPR), redox potentiometry, in vitro electron transfer assays comparing WT and P144L FDX2 with FDXR, protein-protein interaction mapping","journal":"Protein science : a publication of the Protein Society","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal biophysical and biochemical methods (NMR, redox assays, in vitro electron transfer, binding interface mapping) in a single study","pmids":["39467201"],"is_preprint":false},{"year":2025,"finding":"Dominant gain-of-function mutations at the FDX2-NFS1 binding interface (identified in C. elegans and validated biochemically) suppress frataxin deficiency by boosting iron-sulfur cluster levels. Excess wild-type FDX2 inhibits frataxin-stimulated NFS1 (cysteine desulfurase) activity in vitro and blocks Fe-S cluster synthesis in mammalian cell culture, indicating that frataxin and FDX2 compete for the same binding site on NFS1. Partial knockdown of FDX2 (loss of one gene copy) ameliorates the growth defect in frataxin-mutant C. elegans and the ataxia phenotype in a mouse model of Friedreich's ataxia.","method":"Genome-scale forward genetic screen in C. elegans; in vitro NFS1 activity assays with excess FDX2; mammalian cell culture Fe-S cluster synthesis assay; mouse model rescue experiment","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — genetic screen, in vitro biochemical reconstitution, cell-based assays, and in vivo animal model rescue, multiple orthogonal methods across organisms","pmids":["41372402"],"is_preprint":false},{"year":2024,"finding":"FDX2 loss in ovarian cancer cells causes global downregulation of Fe-S-containing proteins and Fe2+ overload, resulting in DNA damage and p53 pathway activation, driving senescence. In p53-deficient cells, FDX2 loss leads to apoptosis rather than senescence. FDX2 loss also sensitizes cells to ferroptosis via compromised redox homeostasis of membrane phospholipids.","method":"Conditional knockout of FDX2 in ovarian cancer cell line; proteomics; DNA damage assays; ferroptosis sensitivity assays; p53 pathway analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean conditional KO with specific cellular phenotypes and pathway placement (p53/senescence/ferroptosis), single lab","pmids":["39151727"],"is_preprint":false},{"year":2025,"finding":"Paramagnetic NMR combined with DFT calculations of the [Fe2S2]2+ cluster of human FDX2 reveals that the two Fe(III) centers are inequivalent due to electron spin density transfer between cluster inorganic sulfide ions and aliphatic carbon atoms via C-H---S-Fe3+ interactions. The magnetic exchange coupling constant between the two Fe3+ ions is estimated at ~386 cm-1.","method":"Paramagnetic NMR spectroscopy; density functional theory quantum chemical calculations","journal":"Inorganic chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — rigorous biophysical/computational characterization of electronic structure, single lab, no functional mutagenesis validation","pmids":["40121555"],"is_preprint":false},{"year":2025,"finding":"A novel FDX2 splicing mutation (c.200+4 A>G) generates a mutant protein with 21 replacement N-terminal residues (replacing exon-2-encoded residues) that likely retains structural integrity (no significant backbone dynamic differences vs WT by NMR), but patient cells with low FDX2 levels show impaired mitochondrial respiration, defects in Fe-S proteins, enhanced mitochondrial iron accumulation, and significantly diminished mitochondrial SOD2 levels.","method":"RNA splicing analysis; NMR structural comparison of mutant vs WT FDX2; mitochondrial respiration assay; Fe-S protein activity assays; mitochondrial iron measurement; western blot for SOD2","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (structural NMR, functional cell assays, protein quantification) in a single patient-based study","pmids":["41372147"],"is_preprint":false}],"current_model":"FDX2 is a mitochondrial [2Fe-2S] ferredoxin that acts as an electron donor at two distinct steps of Fe-S cluster biogenesis: (1) donating electrons to the NFS1/ISD11/Acp cysteine desulfurase complex to drive [2Fe-2S] cluster assembly on ISCU2, competing with frataxin for the NFS1 binding site; and (2) providing electrons for reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 (IBA57-dependent) to form [4Fe-4S] clusters; FDX2 receives electrons from FDXR (ferredoxin reductase) via NADPH, and its C-terminal tail and a conserved loop region (including P144) are critical for FDXR recognition and electron transfer; unlike the paralog FDX1, FDX2 cannot efficiently reduce mitochondrial cytochromes P450 for steroidogenesis, reflecting strict substrate specificity encoded by small conserved sequence motifs."},"narrative":{"mechanistic_narrative":"FDX2 is a mitochondrial [2Fe-2S] ferredoxin that serves as the dedicated electron donor for iron-sulfur (Fe-S) cluster biogenesis, distinct from its paralog FDX1, which instead supports steroidogenesis, heme a biosynthesis, and lipoyl cofactor synthesis [PMID:20547883, PMID:36280795]. FDX2 acts at two sequential steps: it donates electrons to the NFS1/ISD11/Acp cysteine desulfurase complex—binding near its Fe-S cluster more tightly than FDX1 and driving conversion of L-cysteine to L-alanine and sulfide to assemble [2Fe-2S] clusters on ISCU [PMID:28001042], and it subsequently provides electrons for reductive [2Fe-2S] fusion on ISCA1-ISCA2 in an IBA57-dependent manner to mature [4Fe-4S] proteins, a step for which no other cellular reductant substitutes [PMID:32817474]. FDX2 receives electrons from the NADPH-coupled reductase FDXR, and its C-terminal tail mediates this electron transfer; substrate specificity that separates FDX2 from FDX1 is encoded by small conserved sequence motifs, since swapping them exchanges target specificity [PMID:36280795, PMID:39467201]. By competing with frataxin for the NFS1 binding site, FDX2 levels tune cysteine desulfurase output, and reducing FDX2 dosage can ameliorate frataxin-deficiency phenotypes [PMID:41372402]. Loss of FDX2 collapses Fe-S protein maturation, causes mitochondrial iron accumulation, and triggers p53-dependent senescence, apoptosis, and ferroptosis sensitization [PMID:20547883, PMID:39151727]. Loss-of-function and missense FDX2 mutations cause a human mitochondrial disease marked by Fe-S-dependent respiratory chain and aconitase deficiencies, muscle iron accumulation, and impaired mitochondrial respiration [PMID:24281368, PMID:30010796, PMID:41372147].","teleology":[{"year":2010,"claim":"Established that the two human mitochondrial ferredoxins are functionally non-redundant, assigning FDX2 specifically to Fe-S protein and heme A biogenesis rather than steroidogenesis.","evidence":"RNAi depletion of FDX1 vs FDX2 in human cells with biochemical readouts for Fe-S assembly, heme A, steroid conversion, and iron homeostasis","pmids":["20547883"],"confidence":"High","gaps":["Did not resolve which biosynthetic steps FDX2 acts on","No structural basis for substrate discrimination"]},{"year":2013,"claim":"Linked FDX2 to human disease by showing a loss-of-function initiation-codon mutation depletes the protein and cripples Fe-S-dependent respiratory complexes, validating the in vivo requirement for FDX2 in Fe-S biogenesis.","evidence":"Exome sequencing/homozygosity mapping plus enzyme activity assays and western blot in patient muscle and fibroblasts","pmids":["24281368"],"confidence":"Medium","gaps":["Single family/lab","No reconstitution of the mechanistic defect","Genotype-phenotype spectrum unknown"]},{"year":2017,"claim":"Defined the first molecular step of FDX2 action, showing it binds the cysteine desulfurase complex near its Fe-S cluster and donates electrons to assemble [2Fe-2S] clusters on ISCU faster than FDX1.","evidence":"NMR interaction mapping, isothermal titration calorimetry, and in vitro Fe-S assembly assays on ISCU","pmids":["28001042"],"confidence":"High","gaps":["In vitro context only","Did not address downstream [4Fe-4S] maturation","Physiological reductant FDXR not yet incorporated"]},{"year":2018,"claim":"Identified the recurrent P144L missense allele as disease-causing, reinforcing FDX2's essential in vivo role and implicating a specific residue in protein function.","evidence":"Whole exome sequencing, RT-PCR, western blot, and histochemical/iron staining of patient muscle","pmids":["30010796"],"confidence":"Medium","gaps":["Mechanism by which P144L reduces protein/function not defined","Single lab"]},{"year":2020,"claim":"Revealed a second, distinct electron-transfer role for FDX2 in reductive [2Fe-2S] fusion on ISCA1-ISCA2 to build [4Fe-4S] clusters, showing FDX1 and other reductants cannot substitute.","evidence":"In vitro reconstitution of [4Fe-4S] aconitase maturation with defined components, Mössbauer spectroscopy, and complementation assays","pmids":["32817474"],"confidence":"High","gaps":["Structural basis of ISCA1-ISCA2/IBA57 recognition unresolved","Coupling between the two FDX2 steps in cells not defined"]},{"year":2022,"claim":"Pinpointed that small conserved sequence motifs encode the substrate specificity dividing FDX2 (Fe-S maturation) from FDX1 (steroidogenesis, heme a, lipoylation), demonstrated by motif swapping.","evidence":"RNAi depletion, in vitro assays, and domain-swap mutagenesis with functional readouts for each pathway","pmids":["36280795"],"confidence":"High","gaps":["Atomic-level mechanism of motif-encoded recognition not resolved","How motifs dictate partner binding unknown"]},{"year":2024,"claim":"Provided the mechanistic explanation for the P144L disease allele, showing it disrupts FDX2-FDXR recognition and electron transfer, thereby impairing both [2Fe-2S] and [4Fe-4S] assembly, and assigned a functional role to the FDX2 C-terminal tail.","evidence":"NMR/EPR structural characterization, redox potentiometry, and in vitro electron transfer assays comparing WT vs P144L FDX2 with FDXR","pmids":["39467201"],"confidence":"High","gaps":["In cellulo confirmation of the FDXR-interface defect limited","Full FDX2-FDXR complex structure not determined"]},{"year":2024,"claim":"Connected FDX2 loss to cell-fate decisions, showing collapse of Fe-S proteins and iron overload triggers p53-dependent senescence (or apoptosis when p53 is absent) and sensitizes cells to ferroptosis.","evidence":"Conditional FDX2 knockout in ovarian cancer cells with proteomics, DNA damage assays, and ferroptosis/p53 pathway analysis","pmids":["39151727"],"confidence":"Medium","gaps":["Single cancer cell context","Direct link between specific Fe-S client loss and senescence not dissected"]},{"year":2025,"claim":"Established that FDX2 and frataxin compete for the same NFS1 binding site, identifying FDX2 dosage as a therapeutic lever in Friedreich's ataxia.","evidence":"Forward genetic screen in C. elegans, in vitro NFS1 activity assays with excess FDX2, mammalian Fe-S synthesis assays, and mouse Friedreich's ataxia rescue","pmids":["41372402"],"confidence":"High","gaps":["Structural detail of the shared NFS1 interface not fully resolved","Therapeutic window of FDX2 reduction in humans untested"]},{"year":2025,"claim":"Characterized the electronic structure of the FDX2 [Fe2S2]2+ cluster, showing the two Fe(III) centers are inequivalent due to spin density transfer via C-H---S-Fe interactions.","evidence":"Paramagnetic NMR combined with DFT quantum chemical calculations","pmids":["40121555"],"confidence":"Medium","gaps":["No functional mutagenesis validation","Relevance of cluster electronics to electron-transfer kinetics not tested"]},{"year":2025,"claim":"Extended the disease spectrum with a splicing mutation that alters N-terminal residues while preserving fold, linking low FDX2 levels to impaired respiration, Fe-S defects, iron accumulation, and reduced SOD2.","evidence":"RNA splicing analysis, NMR structural comparison, mitochondrial respiration and Fe-S activity assays, and SOD2 western blot in patient cells","pmids":["41372147"],"confidence":"Medium","gaps":["Single patient","Mechanism of SOD2 reduction not established"]},{"year":null,"claim":"How the two spatially and temporally distinct FDX2 electron-donation steps are coordinated in vivo, and the high-resolution structure of FDX2 in complex with FDXR and with the NFS1 desulfurase machinery, remain undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No full structure of FDX2-FDXR or FDX2-NFS1 complexes","Regulation of FDX2 partitioning between ISCU and ISCA steps unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[1,2,6]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[1,2]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,4,5,10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,3]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[8]}],"complexes":[],"partners":["FDXR","NFS1","ISCU","ISCA1","ISCA2","IBA57"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6P4F2","full_name":"Ferredoxin-2, mitochondrial","aliases":["Adrenodoxin-like protein","Ferredoxin-1-like protein"],"length_aa":183,"mass_kda":19.5,"function":"Electron donor, of the core iron-sulfur cluster (ISC) assembly complex, that acts to reduce the persulfide into sulfide during [2Fe-2S] clusters assembly on the scaffolding protein ISCU (PubMed:28001042). The core iron-sulfur cluster (ISC) assembly complex is involved in the de novo synthesis of a [2Fe-2S] cluster, the first step of the mitochondrial iron-sulfur protein biogenesis (By similarity). This process is initiated by the cysteine desulfurase complex (NFS1:LYRM4:NDUFAB1) that produces persulfide which is delivered on the scaffold protein ISCU in a FXN-dependent manner (By similarity). Then this complex is stabilized by FDX2 which provides reducing equivalents to accomplish the [2Fe-2S] cluster assembly (By similarity). Finally, the [2Fe-2S] cluster is transferred from ISCU to chaperone proteins, including HSCB, HSPA9 and GLRX5 (By similarity). Essential for coenzyme Q biosynthesis: together with FDXR, transfers the electrons required for the hydroxylation reaction performed by COQ6 (PubMed:38425362)","subcellular_location":"Mitochondrion; Mitochondrion matrix","url":"https://www.uniprot.org/uniprotkb/Q6P4F2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/FDX2","classification":"Common Essential","n_dependent_lines":868,"n_total_lines":1208,"dependency_fraction":0.7185430463576159},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FDX2","total_profiled":1310},"omim":[{"mim_id":"614585","title":"FERREDOXIN 2; FDX2","url":"https://www.omim.org/entry/614585"},{"mim_id":"605711","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 1; MMDS1","url":"https://www.omim.org/entry/605711"},{"mim_id":"251900","title":"MITOCHONDRIAL MYOPATHY, EPISODIC, WITH OR WITHOUT OPTIC ATROPHY AND REVERSIBLE LEUKOENCEPHALOPATHY; MEOAL","url":"https://www.omim.org/entry/251900"},{"mim_id":"103270","title":"FERREDOXIN REDUCTASE; FDXR","url":"https://www.omim.org/entry/103270"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FDX2"},"hgnc":{"alias_symbol":["MGC19604"],"prev_symbol":["FDX1L"]},"alphafold":{"accession":"Q6P4F2","domains":[{"cath_id":"3.10.20.30","chopping":"71-169","consensus_level":"high","plddt":93.3441,"start":71,"end":169}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6P4F2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6P4F2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6P4F2-F1-predicted_aligned_error_v6.png","plddt_mean":76.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FDX2","jax_strain_url":"https://www.jax.org/strain/search?query=FDX2"},"sequence":{"accession":"Q6P4F2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6P4F2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6P4F2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6P4F2"}},"corpus_meta":[{"pmid":"20547883","id":"PMC_20547883","title":"Humans possess two mitochondrial ferredoxins, Fdx1 and Fdx2, with distinct roles in steroidogenesis, heme, and Fe/S cluster biosynthesis.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20547883","citation_count":321,"is_preprint":false},{"pmid":"36280795","id":"PMC_36280795","title":"Functional spectrum and specificity of mitochondrial ferredoxins FDX1 and FDX2.","date":"2022","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/36280795","citation_count":130,"is_preprint":false},{"pmid":"28001042","id":"PMC_28001042","title":"Human Mitochondrial Ferredoxin 1 (FDX1) and Ferredoxin 2 (FDX2) Both Bind Cysteine Desulfurase and Donate Electrons for Iron-Sulfur Cluster Biosynthesis.","date":"2017","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28001042","citation_count":117,"is_preprint":false},{"pmid":"32817474","id":"PMC_32817474","title":"Mitochondrial [4Fe-4S] protein assembly involves reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 by electron flow from ferredoxin FDX2.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/32817474","citation_count":71,"is_preprint":false},{"pmid":"24281368","id":"PMC_24281368","title":"Deleterious mutation in FDX1L gene is associated with a novel mitochondrial muscle myopathy.","date":"2013","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/24281368","citation_count":70,"is_preprint":false},{"pmid":"30010796","id":"PMC_30010796","title":"A novel complex neurological phenotype due to a homozygous mutation in FDX2.","date":"2018","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/30010796","citation_count":41,"is_preprint":false},{"pmid":"26526668","id":"PMC_26526668","title":"Crystal structure and biochemical characterization of Chlamydomonas FDX2 reveal two residues that, when mutated, partially confer FDX2 the redox potential and catalytic properties of FDX1.","date":"2015","source":"Photosynthesis research","url":"https://pubmed.ncbi.nlm.nih.gov/26526668","citation_count":17,"is_preprint":false},{"pmid":"35079622","id":"PMC_35079622","title":"FDX2 and ISCU Gene Variations Lead to Rhabdomyolysis With Distinct Severity and Iron Regulation.","date":"2022","source":"Neurology. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35079622","citation_count":15,"is_preprint":false},{"pmid":"39151727","id":"PMC_39151727","title":"FDX2, an iron-sulfur cluster assembly factor, is essential to prevent cellular senescence, apoptosis or ferroptosis of ovarian cancer cells.","date":"2024","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39151727","citation_count":12,"is_preprint":false},{"pmid":"39467201","id":"PMC_39467201","title":"Unraveling the molecular determinants of a rare human mitochondrial disorder caused by the P144L mutation of FDX2.","date":"2024","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/39467201","citation_count":8,"is_preprint":false},{"pmid":"34905296","id":"PMC_34905296","title":"Rare presentation of FDX2-related disorder and untargeted global metabolomics findings.","date":"2021","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/34905296","citation_count":7,"is_preprint":false},{"pmid":"38444577","id":"PMC_38444577","title":"Clinical, biochemical and molecular characterization of a new case with FDX2-related mitochondrial disorder: Potential biomarkers and treatment options.","date":"2024","source":"JIMD reports","url":"https://pubmed.ncbi.nlm.nih.gov/38444577","citation_count":6,"is_preprint":false},{"pmid":"37565517","id":"PMC_37565517","title":"Α rare case of myopathy, lactic acidosis, and severe rhabdomyolysis, due to a homozygous mutation of the ferredoxin-2 (FDX2) gene.","date":"2023","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/37565517","citation_count":5,"is_preprint":false},{"pmid":"41372402","id":"PMC_41372402","title":"Mutations in mitochondrial ferredoxin FDX2 suppress frataxin deficiency.","date":"2025","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/41372402","citation_count":3,"is_preprint":false},{"pmid":"40121555","id":"PMC_40121555","title":"Shedding Light on the Electron Delocalization Pathway at the [Fe2S2]2+ Cluster of FDX2.","date":"2025","source":"Inorganic chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/40121555","citation_count":3,"is_preprint":false},{"pmid":"41648530","id":"PMC_41648530","title":"Client distribution between Chlamydomonas FDX1 and FDX2 in carbon, nitrogen and sulfur assimilation.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41648530","citation_count":1,"is_preprint":false},{"pmid":"41372147","id":"PMC_41372147","title":"A novel mutation in FDX2 provides insights into the pathogenesis of MEOAL mitochondrial neuromuscular disease.","date":"2025","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41372147","citation_count":0,"is_preprint":false},{"pmid":"42208897","id":"PMC_42208897","title":"The iron-sulfur cluster assembly factor FDX2 is required for tumor initiation but not for growth of established tumors in transplantation models.","date":"2026","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/42208897","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11345,"output_tokens":3330,"usd":0.041993,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10881,"output_tokens":3758,"usd":0.074177,"stage2_stop_reason":"end_turn"},"total_usd":0.11617,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"FDX2 (Fdx2), but not FDX1 (Fdx1/adrenodoxin), is essential for heme A and Fe/S protein biosynthesis in human mitochondria. FDX2 deficiency impairs Fe/S protein biogenesis, leading to increased cellular iron uptake and iron accumulation in mitochondria. Conversely, FDX2 is unable to efficiently reduce mitochondrial cytochromes P450 or convert steroids, functions specific to FDX1.\",\n      \"method\": \"RNAi-mediated depletion of FDX1 or FDX2 in human cells, with biochemical readouts for heme A, Fe/S cluster assembly, steroid conversion, and iron homeostasis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockdown with multiple orthogonal biochemical readouts, independently establishing substrate specificity of FDX2 vs FDX1\",\n      \"pmids\": [\"20547883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Both FDX1 and FDX2 bind the cysteine desulfurase complex (NFS1/ISD11/Acp) via residues near their Fe-S clusters, but FDX2 binds the complex more tightly than FDX1 (by isothermal titration calorimetry). In vitro, reduced FDX2 supports Fe-S cluster assembly on ISCU at a faster rate than FDX1. FDX2 donates electrons to the cysteine desulfurase complex, resulting in conversion of L-cysteine to L-alanine and sulfide generation.\",\n      \"method\": \"NMR spectroscopy (protein-protein interaction mapping), isothermal titration calorimetry, in vitro Fe-S cluster assembly assay on ISCU\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal in vitro methods (NMR, ITC, reconstitution assay) in a single study\",\n      \"pmids\": [\"28001042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FDX2, together with its reductase FDXR (NADPH-coupled), provides electrons required for reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 in an IBA57-dependent manner, enabling maturation of mitochondrial [4Fe-4S] proteins. This electron transfer step is distinct from FDX2's earlier role in [2Fe-2S] cluster synthesis on ISCU2. FDX1 and other cellular reducing systems cannot substitute for FDX2 in this step.\",\n      \"method\": \"In vitro reconstitution of [4Fe-4S] aconitase maturation without artificial reductants, using purified components; Mössbauer spectroscopy; biochemical complementation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with defined components, multiple spectroscopic validations, specificity confirmed by negative controls (FDX1, other reductants)\",\n      \"pmids\": [\"32817474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FDX2, but not FDX1, is required for Fe-S protein maturation; FDX1 is specific for steroidogenesis, heme a biosynthesis, and lipoyl cofactor biosynthesis (providing electrons to lipoyl synthase). The distinct substrate specificity of each ferredoxin is determined by small conserved sequence motifs; swapping these motifs exchanges their target specificities.\",\n      \"method\": \"RNAi depletion in human cells, in vitro biochemical assays, domain-swap mutagenesis, functional assays for steroidogenesis/lipoylation/Fe-S assembly\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including mutagenesis, in vitro assays, and cell-based depletion; replicates and extends earlier PNAS 2010 findings\",\n      \"pmids\": [\"36280795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A homozygous loss-of-function mutation in FDX1L (FDX2; c.1A>T disrupting the ATG initiation codon) causes severe reduction of Fdx2 protein in patient muscle and fibroblast mitochondria, resulting in severely impaired activities of Fe-S-dependent respiratory chain complexes I, II, III and mitochondrial aconitase, establishing FDX2 as the second component of the Fe-S cluster biogenesis machinery in human muscle.\",\n      \"method\": \"Exome sequencing + homozygosity mapping; enzyme activity assays in patient skeletal muscle; western blot of patient mitochondria\",\n      \"journal\": \"European journal of human genetics : EJHG\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function patient mutation with specific biochemical phenotype (enzyme activities) and protein quantification; single lab, no in vitro reconstitution\",\n      \"pmids\": [\"24281368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A homozygous missense mutation in FDX2 (c.431C>T, p.P144L) causes severely reduced FDX2 protein expression (normal mRNA, reduced protein by western blot) in patient muscle, with an unusual pattern of succinate dehydrogenase and cytochrome c oxidase deficiency and iron accumulation on muscle biopsy, confirming FDX2's essential role in Fe-S cluster biogenesis in vivo.\",\n      \"method\": \"Genetic mapping + whole exome sequencing; RT-PCR; western blot of patient muscle; muscle biopsy with histochemical and iron staining\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient loss-of-function with protein quantification and specific biochemical readouts, single lab\",\n      \"pmids\": [\"30010796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The pathogenic P144L mutation of FDX2 negatively affects the FDXR-dependent electron transfer pathway from NADPH to FDX2 by altering the protein-protein recognition between FDX2 and its physiological electron donor FDXR, thereby reducing FDX2's capacity to assemble both [2Fe-2S] and [4Fe-4S] clusters. The C-terminal tail of FDX2 plays a functional role in electron transfer between FDX2 and FDXR.\",\n      \"method\": \"Structural characterization (NMR, EPR), redox potentiometry, in vitro electron transfer assays comparing WT and P144L FDX2 with FDXR, protein-protein interaction mapping\",\n      \"journal\": \"Protein science : a publication of the Protein Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal biophysical and biochemical methods (NMR, redox assays, in vitro electron transfer, binding interface mapping) in a single study\",\n      \"pmids\": [\"39467201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Dominant gain-of-function mutations at the FDX2-NFS1 binding interface (identified in C. elegans and validated biochemically) suppress frataxin deficiency by boosting iron-sulfur cluster levels. Excess wild-type FDX2 inhibits frataxin-stimulated NFS1 (cysteine desulfurase) activity in vitro and blocks Fe-S cluster synthesis in mammalian cell culture, indicating that frataxin and FDX2 compete for the same binding site on NFS1. Partial knockdown of FDX2 (loss of one gene copy) ameliorates the growth defect in frataxin-mutant C. elegans and the ataxia phenotype in a mouse model of Friedreich's ataxia.\",\n      \"method\": \"Genome-scale forward genetic screen in C. elegans; in vitro NFS1 activity assays with excess FDX2; mammalian cell culture Fe-S cluster synthesis assay; mouse model rescue experiment\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — genetic screen, in vitro biochemical reconstitution, cell-based assays, and in vivo animal model rescue, multiple orthogonal methods across organisms\",\n      \"pmids\": [\"41372402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FDX2 loss in ovarian cancer cells causes global downregulation of Fe-S-containing proteins and Fe2+ overload, resulting in DNA damage and p53 pathway activation, driving senescence. In p53-deficient cells, FDX2 loss leads to apoptosis rather than senescence. FDX2 loss also sensitizes cells to ferroptosis via compromised redox homeostasis of membrane phospholipids.\",\n      \"method\": \"Conditional knockout of FDX2 in ovarian cancer cell line; proteomics; DNA damage assays; ferroptosis sensitivity assays; p53 pathway analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean conditional KO with specific cellular phenotypes and pathway placement (p53/senescence/ferroptosis), single lab\",\n      \"pmids\": [\"39151727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Paramagnetic NMR combined with DFT calculations of the [Fe2S2]2+ cluster of human FDX2 reveals that the two Fe(III) centers are inequivalent due to electron spin density transfer between cluster inorganic sulfide ions and aliphatic carbon atoms via C-H---S-Fe3+ interactions. The magnetic exchange coupling constant between the two Fe3+ ions is estimated at ~386 cm-1.\",\n      \"method\": \"Paramagnetic NMR spectroscopy; density functional theory quantum chemical calculations\",\n      \"journal\": \"Inorganic chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — rigorous biophysical/computational characterization of electronic structure, single lab, no functional mutagenesis validation\",\n      \"pmids\": [\"40121555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel FDX2 splicing mutation (c.200+4 A>G) generates a mutant protein with 21 replacement N-terminal residues (replacing exon-2-encoded residues) that likely retains structural integrity (no significant backbone dynamic differences vs WT by NMR), but patient cells with low FDX2 levels show impaired mitochondrial respiration, defects in Fe-S proteins, enhanced mitochondrial iron accumulation, and significantly diminished mitochondrial SOD2 levels.\",\n      \"method\": \"RNA splicing analysis; NMR structural comparison of mutant vs WT FDX2; mitochondrial respiration assay; Fe-S protein activity assays; mitochondrial iron measurement; western blot for SOD2\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (structural NMR, functional cell assays, protein quantification) in a single patient-based study\",\n      \"pmids\": [\"41372147\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FDX2 is a mitochondrial [2Fe-2S] ferredoxin that acts as an electron donor at two distinct steps of Fe-S cluster biogenesis: (1) donating electrons to the NFS1/ISD11/Acp cysteine desulfurase complex to drive [2Fe-2S] cluster assembly on ISCU2, competing with frataxin for the NFS1 binding site; and (2) providing electrons for reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 (IBA57-dependent) to form [4Fe-4S] clusters; FDX2 receives electrons from FDXR (ferredoxin reductase) via NADPH, and its C-terminal tail and a conserved loop region (including P144) are critical for FDXR recognition and electron transfer; unlike the paralog FDX1, FDX2 cannot efficiently reduce mitochondrial cytochromes P450 for steroidogenesis, reflecting strict substrate specificity encoded by small conserved sequence motifs.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FDX2 is a mitochondrial [2Fe-2S] ferredoxin that serves as the dedicated electron donor for iron-sulfur (Fe-S) cluster biogenesis, distinct from its paralog FDX1, which instead supports steroidogenesis, heme a biosynthesis, and lipoyl cofactor synthesis [#0, #3]. FDX2 acts at two sequential steps: it donates electrons to the NFS1/ISD11/Acp cysteine desulfurase complex—binding near its Fe-S cluster more tightly than FDX1 and driving conversion of L-cysteine to L-alanine and sulfide to assemble [2Fe-2S] clusters on ISCU [#1], and it subsequently provides electrons for reductive [2Fe-2S] fusion on ISCA1-ISCA2 in an IBA57-dependent manner to mature [4Fe-4S] proteins, a step for which no other cellular reductant substitutes [#2]. FDX2 receives electrons from the NADPH-coupled reductase FDXR, and its C-terminal tail mediates this electron transfer; substrate specificity that separates FDX2 from FDX1 is encoded by small conserved sequence motifs, since swapping them exchanges target specificity [#3, #6]. By competing with frataxin for the NFS1 binding site, FDX2 levels tune cysteine desulfurase output, and reducing FDX2 dosage can ameliorate frataxin-deficiency phenotypes [#7]. Loss of FDX2 collapses Fe-S protein maturation, causes mitochondrial iron accumulation, and triggers p53-dependent senescence, apoptosis, and ferroptosis sensitization [#0, #8]. Loss-of-function and missense FDX2 mutations cause a human mitochondrial disease marked by Fe-S-dependent respiratory chain and aconitase deficiencies, muscle iron accumulation, and impaired mitochondrial respiration [#4, #5, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established that the two human mitochondrial ferredoxins are functionally non-redundant, assigning FDX2 specifically to Fe-S protein and heme A biogenesis rather than steroidogenesis.\",\n      \"evidence\": \"RNAi depletion of FDX1 vs FDX2 in human cells with biochemical readouts for Fe-S assembly, heme A, steroid conversion, and iron homeostasis\",\n      \"pmids\": [\"20547883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which biosynthetic steps FDX2 acts on\", \"No structural basis for substrate discrimination\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Linked FDX2 to human disease by showing a loss-of-function initiation-codon mutation depletes the protein and cripples Fe-S-dependent respiratory complexes, validating the in vivo requirement for FDX2 in Fe-S biogenesis.\",\n      \"evidence\": \"Exome sequencing/homozygosity mapping plus enzyme activity assays and western blot in patient muscle and fibroblasts\",\n      \"pmids\": [\"24281368\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single family/lab\", \"No reconstitution of the mechanistic defect\", \"Genotype-phenotype spectrum unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the first molecular step of FDX2 action, showing it binds the cysteine desulfurase complex near its Fe-S cluster and donates electrons to assemble [2Fe-2S] clusters on ISCU faster than FDX1.\",\n      \"evidence\": \"NMR interaction mapping, isothermal titration calorimetry, and in vitro Fe-S assembly assays on ISCU\",\n      \"pmids\": [\"28001042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vitro context only\", \"Did not address downstream [4Fe-4S] maturation\", \"Physiological reductant FDXR not yet incorporated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified the recurrent P144L missense allele as disease-causing, reinforcing FDX2's essential in vivo role and implicating a specific residue in protein function.\",\n      \"evidence\": \"Whole exome sequencing, RT-PCR, western blot, and histochemical/iron staining of patient muscle\",\n      \"pmids\": [\"30010796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which P144L reduces protein/function not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed a second, distinct electron-transfer role for FDX2 in reductive [2Fe-2S] fusion on ISCA1-ISCA2 to build [4Fe-4S] clusters, showing FDX1 and other reductants cannot substitute.\",\n      \"evidence\": \"In vitro reconstitution of [4Fe-4S] aconitase maturation with defined components, Mössbauer spectroscopy, and complementation assays\",\n      \"pmids\": [\"32817474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ISCA1-ISCA2/IBA57 recognition unresolved\", \"Coupling between the two FDX2 steps in cells not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Pinpointed that small conserved sequence motifs encode the substrate specificity dividing FDX2 (Fe-S maturation) from FDX1 (steroidogenesis, heme a, lipoylation), demonstrated by motif swapping.\",\n      \"evidence\": \"RNAi depletion, in vitro assays, and domain-swap mutagenesis with functional readouts for each pathway\",\n      \"pmids\": [\"36280795\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level mechanism of motif-encoded recognition not resolved\", \"How motifs dictate partner binding unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the mechanistic explanation for the P144L disease allele, showing it disrupts FDX2-FDXR recognition and electron transfer, thereby impairing both [2Fe-2S] and [4Fe-4S] assembly, and assigned a functional role to the FDX2 C-terminal tail.\",\n      \"evidence\": \"NMR/EPR structural characterization, redox potentiometry, and in vitro electron transfer assays comparing WT vs P144L FDX2 with FDXR\",\n      \"pmids\": [\"39467201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In cellulo confirmation of the FDXR-interface defect limited\", \"Full FDX2-FDXR complex structure not determined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected FDX2 loss to cell-fate decisions, showing collapse of Fe-S proteins and iron overload triggers p53-dependent senescence (or apoptosis when p53 is absent) and sensitizes cells to ferroptosis.\",\n      \"evidence\": \"Conditional FDX2 knockout in ovarian cancer cells with proteomics, DNA damage assays, and ferroptosis/p53 pathway analysis\",\n      \"pmids\": [\"39151727\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cancer cell context\", \"Direct link between specific Fe-S client loss and senescence not dissected\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established that FDX2 and frataxin compete for the same NFS1 binding site, identifying FDX2 dosage as a therapeutic lever in Friedreich's ataxia.\",\n      \"evidence\": \"Forward genetic screen in C. elegans, in vitro NFS1 activity assays with excess FDX2, mammalian Fe-S synthesis assays, and mouse Friedreich's ataxia rescue\",\n      \"pmids\": [\"41372402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural detail of the shared NFS1 interface not fully resolved\", \"Therapeutic window of FDX2 reduction in humans untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Characterized the electronic structure of the FDX2 [Fe2S2]2+ cluster, showing the two Fe(III) centers are inequivalent due to spin density transfer via C-H---S-Fe interactions.\",\n      \"evidence\": \"Paramagnetic NMR combined with DFT quantum chemical calculations\",\n      \"pmids\": [\"40121555\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional mutagenesis validation\", \"Relevance of cluster electronics to electron-transfer kinetics not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended the disease spectrum with a splicing mutation that alters N-terminal residues while preserving fold, linking low FDX2 levels to impaired respiration, Fe-S defects, iron accumulation, and reduced SOD2.\",\n      \"evidence\": \"RNA splicing analysis, NMR structural comparison, mitochondrial respiration and Fe-S activity assays, and SOD2 western blot in patient cells\",\n      \"pmids\": [\"41372147\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single patient\", \"Mechanism of SOD2 reduction not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the two spatially and temporally distinct FDX2 electron-donation steps are coordinated in vivo, and the high-resolution structure of FDX2 in complex with FDXR and with the NFS1 desulfurase machinery, remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full structure of FDX2-FDXR or FDX2-NFS1 complexes\", \"Regulation of FDX2 partitioning between ISCU and ISCA steps unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [1, 2, 6]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 4, 5, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"FDXR\", \"NFS1\", \"ISCU\", \"ISCA1\", \"ISCA2\", \"IBA57\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}